1. Field of the Invention
The present invention relates to an intermediate for an optical recording medium that has a central mounting hole formed in a central portion thereof and at least one kind of functional layer formed on one side thereof, for use in at least one of information recording and information reproduction, a mold for manufacturing the intermediate for an optical recording medium, a molding apparatus including the mold, and a method of manufacturing the optical recording medium by using the intermediate for an optical recording medium.
2. Description of the Related Art
For example, in a method of manufacturing an optical recording medium, such as a CD (Compact Disk) or a DVD (Digital Versatile Disk), first, a disk-shaped substrate DP having a shape shown in FIG. 20 is molded by injecting resin into a mold having a stamper set therein. In this step, the central portion of the disk-shaped substrate DP is blanked by a gate cutter incorporated in the mold, whereby a central mounting hole (also used as a central mounting hole of the optical recording medium) MH is formed in the central portion of the disk-shaped substrate DP. Further, micro asperities (not shown) such as grooves are formed in an area (recording area RA) on one surface (upper surface as viewed in FIG. 20) of the disk-shaped substrate DP, where functional layers, referred to hereinafter, are to be formed. Furthermore, an annular projection (so-called stock ring) SR is formed on the other surface (lower surface as viewed in FIG. 20) of the disk-shaped substrate DP. The annular projection SR is formed in a zone between a chucking area CA adjacent to the central mounting hole MH toward the inner periphery of the disk-shaped substrate DP and the recording area RA. Molded disk-shaped substrates DP are stored in a state stacked on a stacker 51 with the central mounting hole MH of each disk-shaped substrate DP being fitted on a stacker pole 51a of the stacker 51. In this case, the disk-shaped substrates DP are stacked with spaces created therebetween by the annular projections SR. Therefore, even if vibrations are applied to the disk-shaped substrates DP in this state, the disk-shaped substrates DP are prevented from being greatly inclined, so that interference between the disk-shaped substrates DP can be avoided, which prevents the surfaces of the disk-shaped substrates DP from being damaged or flawed.
Then, the disk-shaped substrates DP are sequentially taken out from the stacker 51, and various functional layers (reflection layer, recording layer, protective layer, etc.) are sequentially formed in the recording area RA on the one surface of each disk-shaped substrate DP to thereby complete an optical recording medium (not shown). Thereafter, the completed optical recording media are stored on the stacker 51 similarly to the disk-shaped substrates DP. In the step of forming the functional layers, at least one of the functional layers (e.g. the protective layer) is formed by coating resin by the spin coating method and then curing the coated resin by a predetermined curing treatment. In this case, as shown in FIG. 20, a method is employed which coats resin using a disk-shaped member DI as a resin coating-assisting member (see Japanese Laid-Open Patent Publication (Kokai) No. 10-249264), because this method facilitates formation of functional layers (resin layers) uniform in thickness particularly in radial directions. Basically in this method, the disk-shaped member DI is placed on a disk-shaped substrate DP such that the member DI covers the central mounting hole MH as shown in FIG. 20, and then the resin R is dropped from a nozzle NZ onto the disk-shaped member DI for spin coating. Thereafter, the disk-shaped member DI is removed from the disk-shaped substrate DP as shown in FIG. 21, and the disk-shaped substrate DP coated with the resin R up to the outer periphery of the upper surface thereof is conveyed to a site for executing the curing treatment. Since the resin R remains uncured during the conveyance, the disk-shaped substrate DP is carried with an uncoated area (adjacent to the central mounting hole MH) that was covered by the disk-shaped member DI being sucked by a suction device (not shown) or with the central mounting hole MH being made use of by a mechanical chuck (not shown).
However, in the above described method of manufacturing an optical recording medium, maintenance of the used disk-shaped member DI (e.g. cleaning of the disk-shaped member DI having resin R stuck thereto) is troublesome. To overcome this problem, the present inventors developed a method of manufacturing an optical recording medium using an intermediate therefor which is not formed with a central mounting hole MH in its central portion. In this method, first, an intermediate ME, shown in FIG. 23, for a disk-shaped substrate, is molded by the same method as employed in manufacturing the disk-shaped substrate DP. In this step, a central mounting hole MH is not formed through the intermediate ME, but micro asperities (not shown) such as grooves are formed in one surface (upper surface as viewed in FIG. 23) thereof, and an annular projection SR is formed on the other surface (lower surface as viewed in FIG. 23), similarly to the case of manufacturing the disk-shaped substrate DP. Then, various functional layers (reflection layer, recording layer, protective layer, etc.) are sequentially formed in a recording area RA on the one surface of the intermediate ME. When the spin coating method is employed to apply resin R to the intermediate ME for formation of each of the functional layers, the resin R is dropped from a nozzle NZ onto the central portion of the intermediate for spin coating, so that a layer of the resin R is coated which has a substantially uniform thickness in radial directions, as shown in FIG. 24. Thereafter, the central portion of the intermediate ME having all the functional layers (hereinafter collectively referred to as “the layer FL”) formed on the one surface thereof is blanked by presswork (blanking using a punch) to form a central mounting hole MH. Thus, an optical recording medium 1 having the central portion thereof formed with the central mounting hole MH, as shown in FIG. 9, is completed. According to this method of manufacturing an optical recording medium, since the disk-shaped member DI is not used for spin coating, it is possible to save time and labor required for troublesome maintenance of the disk-shaped member DI.
However, from the study of the above described method of manufacturing an optical recording medium, the present inventors found out the following problems to be solved: In the manufacturing method, first, the intermediate ME without the central mounting hole MH is molded, and then the layer FL is formed on the intermediate ME, whereafter the central mounting hole MH is formed by presswork. Therefore, in a case where the spin coating method is employed for formation of functional layers, since the central mounting hole MH is not yet formed in the intermediate ME when the intermediate ME coated with uncured resin R need be conveyed to the site for carrying out curing treatment, it is difficult to use the aforementioned mechanical chuck. Further, since the area that is not coated with the resin R does not exist on the intermediate ME, it is also difficult to use the aforementioned suction device. Therefore, improvement in this point is desirable. In this connection, a method can be contemplated which uses a device additionally provided for partially curing the resin R to cure part of the resin R on the central portion of the intermediate ME, for allowing the suction device to suck the cured portion. However, this method necessitates the device for partially curing the resin R, which requires new expenditures on plant and equipment. Further, since the step of partially curing the resin R is added, manufacturing time is increased, causing reduced production of optical recording media 1 per unit time, resulting in an increase in manufacturing costs.
Further, in this method of manufacturing an optical recording medium, since the central mounting hole MH is not formed until the presswork is completed in a final step, it is impossible to use the stacker 51 conventionally used, for storing molded intermediates ME or holding intermediates ME having passed through one processing step until the succeeding processing step starts. To overcome this problem, a method of storing intermediates ME can be considered which uses a stacker 61 having a plurality of stack poles 61a (three stack poles 61a in the illustrated example) erected on the same circumference as shown in FIG. 25 to store intermediates ME therein in a stacked manner. In this case, the intermediates ME held within the stack poles 61a, 61a, 61a have respective outer peripheral edges thereof supported by the stack poles 61a, 61a, 61a. Although not shown, another method can be considered which uses a storage case having a plurality of grooves formed therein at equal space intervals, each for receiving the outer peripheral edge of an intermediate ME, to store intermediates ME in a vertical position in parallel with each other in the side-by-side arrangement. In the former storing method, however, since each intermediate ME has its outer peripheral edge supported only by the stack poles 61a, 61a, 61a, when vibrations are applied to a plurality of intermediates ME stacked one upon another, the intermediates ME easily lose their balance and are tilted as shown in FIG. 26. This also raises a problem to be solved. In the latter storing method, the area occupied by the storage case is laterally increased in accordance with an increase in the number of stored intermediates ME, and hence it is difficult to allocate enough space for the storage case when the number of intermediates ME to be stored is large.
Moreover, in this method of manufacturing an optical recording medium, the central portion of an intermediate ME to be blanked by presswork to form the central mounting hole MH has the same thickness as that of a portion surrounding the central portion, and hence burrs can be formed on the inner peripheral surfaces of the intermediate ME and the layer FL defining the central mounting hole MH, during blanking using a punch. If burrs are formed, the optical recording medium 1 is likely to be mounted on a drive device in an off-center position. In such a case, the optical recording medium 1 vibrates when it is rotated, which makes it difficult to record information thereon or reproduce information therefrom, with accuracy. Therefore, improvement in this point is desirable.